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Cardiff Blues v Northampton</div>
A foot injury denies Martyn Williams the chance to face Northampton at Ricoh Arena, his back-row place filled by Robin Sowden-Taylor.
The Blues welcome back Leigh Halfpenny, Tom Shanklin and Jamie Roberts from Wales Six Nations duty, while Gethin Jenkins also returns in the forwards.
Paul Diggin replaces Sean Lamont on the Saints wing with Stephen Myler preferred to Barry Everitt at fly-half.
Tom Smith, Dylan Hartley and Euan Murray return in a new-look front row.
Argentine second row Ignacio Fernandez Lobbe and flanker Scott Gray also come in to freshen up a side that lost 32-27 to London Irish last time out.
Wales squad members Bradley Davies and John Yapp return to the Blues bench after winning caps against Italy but number eight Andy Powell is still absent after injured a thigh muscle last Friday.
Blues coach Dai Young hopes his side can go a step further than last season.
The Blues failed to reach the same stage last year and Young does not want to risk them blowing the chance of making the final by thinking too far ahead.
"We know how big this game is and we want to go one step further and get to the final," said Young.
"We are certainly not talking about the final or winning it, we are just talking about Northampton.
"They are a quality outfit. We know how hard it is going to be, but if we can reach the heights that we've reached for most of the season, I'm confident we will come away with the result."
Northampton director of rugby Jim Mallinder is also expecting a tough encounter and also praised the quality of the opposition.
"We certainly know that we will have to be at our very best to beat them. They've got top-class players in their squad who are household names like Gethin Jenkins and Tom Shanklin as well as plenty of others with lots of experience like Xavier Rush, Paul ***o and Ben Blair," he said.
"But we have played well in our last few games and with our international players returning we have some selection dilemmas.
"I've been delighted with the way the internationals have played in the Six Nations, but have also been delighted with how the players who have come into the Saints side have performed.
"There were certainly several tough decisions over who will play on Saturday."
Route to the semi-final:
The Blues beat Leicester Tigers, Bath and the Sale Sharks on their way to reaching the semi-final, which is being held at the Ricoh Arena.
Northampton Saints, eighth in the Guinness Premiership, made it to the last four by beating Bristol and the Scarlets in their group.
Cardiff Blues: Blair; Halfpenny, Shanklin, Roberts, James; N Robinson, Spice; Jenkins, G Williams, Filise, D Jones, ***o (capt), Molitika, Sowden Taylor, Rush.
Replacements: Yapp, Rhys Thomas, B Davies, Morgan, Rees, Sweeney, J Robinson.
Northampton Saints: Foden; Diggin, Ansbro, Downey, Reihana (capt); Myler, Dickson; Smith, Hartley, Murray, Fernandez Lobbe, Kruger, Best, Gray, Wilson.
Replacements: Sharman, Tonga'uiha, Lawes, Easter, Dickens, Everitt, Mayor.
BBC Sport
Cardiff Blues v Northampton</div>
A foot injury denies Martyn Williams the chance to face Northampton at Ricoh Arena, his back-row place filled by Robin Sowden-Taylor.
The Blues welcome back Leigh Halfpenny, Tom Shanklin and Jamie Roberts from Wales Six Nations duty, while Gethin Jenkins also returns in the forwards.
Paul Diggin replaces Sean Lamont on the Saints wing with Stephen Myler preferred to Barry Everitt at fly-half.
Tom Smith, Dylan Hartley and Euan Murray return in a new-look front row.
Argentine second row Ignacio Fernandez Lobbe and flanker Scott Gray also come in to freshen up a side that lost 32-27 to London Irish last time out.
Wales squad members Bradley Davies and John Yapp return to the Blues bench after winning caps against Italy but number eight Andy Powell is still absent after injured a thigh muscle last Friday.
Blues coach Dai Young hopes his side can go a step further than last season.
The Blues failed to reach the same stage last year and Young does not want to risk them blowing the chance of making the final by thinking too far ahead.
"We know how big this game is and we want to go one step further and get to the final," said Young.
"We are certainly not talking about the final or winning it, we are just talking about Northampton.
"They are a quality outfit. We know how hard it is going to be, but if we can reach the heights that we've reached for most of the season, I'm confident we will come away with the result."
Northampton director of rugby Jim Mallinder is also expecting a tough encounter and also praised the quality of the opposition.
"We certainly know that we will have to be at our very best to beat them. They've got top-class players in their squad who are household names like Gethin Jenkins and Tom Shanklin as well as plenty of others with lots of experience like Xavier Rush, Paul ***o and Ben Blair," he said.
"But we have played well in our last few games and with our international players returning we have some selection dilemmas.
"I've been delighted with the way the internationals have played in the Six Nations, but have also been delighted with how the players who have come into the Saints side have performed.
"There were certainly several tough decisions over who will play on Saturday."
Route to the semi-final:
The Blues beat Leicester Tigers, Bath and the Sale Sharks on their way to reaching the semi-final, which is being held at the Ricoh Arena.
Northampton Saints, eighth in the Guinness Premiership, made it to the last four by beating Bristol and the Scarlets in their group.
Cardiff Blues: Blair; Halfpenny, Shanklin, Roberts, James; N Robinson, Spice; Jenkins, G Williams, Filise, D Jones, ***o (capt), Molitika, Sowden Taylor, Rush.
Replacements: Yapp, Rhys Thomas, B Davies, Morgan, Rees, Sweeney, J Robinson.
Northampton Saints: Foden; Diggin, Ansbro, Downey, Reihana (capt); Myler, Dickson; Smith, Hartley, Murray, Fernandez Lobbe, Kruger, Best, Gray, Wilson.
Replacements: Sharman, Tonga'uiha, Lawes, Easter, Dickens, Everitt, Mayor.
BBC Sport
